Stereo vision is the extraction of three-dimensional information from two or more digital images. It is particularly important to many industrial applications. For example, stereoscopic images are used to analyze and evaluate components of semiconductor chips. Microelectronics are typically made and packaged in large volumes in high-precision manufacturing environments. It is important for each of completed object to be inspected. Because of the small size of the components and large volume of small pieces, the inspection must be automated. Three-dimensional vision is essential because the inspection involves examining specific critical three-dimensional features of each package.
In traditional stereo vision, two cameras are usually displaced horizontally from one another in a manner similar to human binocular vision. For example, U.S. Pat. No. 8,107,719 discloses a vision system for the three-dimensional metrology of a rapidly moving semiconductor or packaged electronic objects. The system includes three cameras mounted to a back plate. The cameras are disposed on the same plane and are symmetrically arranged so that one camera is disposed at an acute angle, another camera is disposed at an obtuse angle and the third camera is disposed orthogonally relative to the field of view. This arrangement allows for the determination of the three-dimensional imaging and analysis of an object.
U.S. Pat. No. 8,885,040 discloses a stereo vision inspection system for ball and like protrusions of electronic components. It describes a method of full calibration of the stereo vision system, by which both the interior and the exterior parameters of the stereo cameras are determined. A rectified stereo camera system is then established. Conjugate points are detected on the rectified images and are used for reconstruction of the three-dimensional location information. The information is further used for three-dimensional measurement.
U.S. Pat. No. 9,594,028 discloses an improved stereo vision inspection system for determining coplanarity of three-dimensional features in integrated circuit packages. The system includes two side view cameras with tiltable lens arranged according to the Scheimpflug principle. The system improves the accuracy of the measurement by producing well-focused images of uniform light intensity.
In the above-mentioned systems, the stereo cameras are all arranged on one plane. While suitable for some uses, these systems have limitations. For example, these systems are not capable of inspecting the lead foot angle of all the leads in a Quad Flat Package (QFP) or similar device. They cannot detect the lead foot angle or a bend in a lead that extends parallel (or nearly parallel) to the cameras plane. As a QFP device has leads extending out on all four sides of its substrate, inspection of the lead foot angle of all the leads requires viewing the device at multiple angles. The inspection of the lead foot angle of all the leads is essential as a bent lead can affect reliability of the circuit and lead to a defective product.
A need, therefore, exists for an improved system and method that overcomes these limitations. It is, therefore, a motivation of the present invention to provide a three-dimensional vision inspection system that allows complete inspection of the lead foot angles of all the leads in the QFP devices. The system should be capable of rapidly inspecting a high volume of objects with high accuracy, precision and reliability.